Structuring restricted amorphous molecular chains in the reinforced cellulose film by uniaxial stretching.

The construction of the preferred orientation structure by stretching is an efficient strategy to fabricate high-performance cellulose film and it is still an open issue whether crystalline structure or amorphous molecular chain is the key factor in determining the enhanced mechanical performance. Herein, uniaxial stretching with constant width followed by drying in a stretching state was carried out to cellulose hydrogels with physical and chemical double cross-linking networks, achieving high-performance regenerated cellulose films (RCFs) with an impressive tensile strength of 154.5 MPa and an elastic modulus of 5.4 GPa. The hierarchical structure of RCFs during uniaxial stretching and drying was systematically characterized from micro- to nanoscale, including microscopic morphology, crystalline structure as well as relaxation behavior at a molecular level. The two-dimensional correlation spectra of dynamic mechanical analysis and Havriliak-Negami fitting results verified that the enhanced mechanical properties of RCFs were mainly attributed to the stretch-induced tight packing and restricted relaxation of amorphous molecular chains. The new insight concerning the contribution of molecular chains in the amorphous region to the enhancement of mechanical performance for RCFs is expected to provide valuable guidance for designing and fabricating high-performance eco-friendly cellulose-based films.

Peelable Microwave Absorption Coating with Reusable and Anticorrosion Merits.

The peelable microwave absorption (MA) coating with reversible adhesion for stable presence on substrates and easy release without any residuals is highly desired in temporary electromagnetic protection, which can quickly enter and disengage the electromagnetic protection state according to the real-time changeable harsh surroundings. On the contrary, with the incorporation of abundant absorbent to achieve excellent MA ability, the tunable adhesion and sufficient cohesion are extremely challenging to fulfill the above requirement. The reported peelable coatings still have problems in controlling adhesion/cohesion strength and coating release, facing substantial residuals after peeling even using complex chemical modification or abundant additives. Herein, a peelable MA coating based on the block characteristics of polar and nonpolar segments of poly(styrene-(ethylene-co-butylene)-styrene) (SEBS) is successfully developed. The polyaniline-decorated carbon nanotube as a microwave absorber plays a positive influence on the adhesion/cohesion of the coating due to bonding interaction. The competitive effective absorption bandwidth (EAB) of 8.8 GHz and controllable yet reversible adhesion release on various substrates and complex surfaces have been achieved. The reusability endows peelable MA coating with 93% retention of EAB even after ten coating-peeling cycles. The coating with excellent chemical and adhesion stability can effectively protect substrates from salt/acid/alkali corrosion, showing over 98% retention of EAB even after 8 h of accelerated corrosion. Our peelable MA coating via a general yet reliable approach provides a prospect for temporary electromagnetic protection.

Self-standing boron nitride bulks enabled by liquid metals for thermal management.

Thermally conductive materials (TCMs) are highly desirable for thermal management applications to tackle the "overheating" concerns in the electronics industry. Despite recent progress, the development of high performance TCMs integrated with an in-plane thermal conductivity (TC) higher than 50.0 W (m K)-1 and a through-plane TC greater than 10.0 W (m K)-1 is still challenging. Herein, self-standing liquid metal@boron nitride (LM@BN) bulks with ultrahigh in-plane TC and through-plane TC were reported for the first time. In the LM@BN bulks, LM could serve as a bonding and thermal linker among the oriented BN platelets, thus remarkably accelerating heat transfer across the whole system. Benefiting from the formation of a unique structure, the LM@BN bulk achieved an ultrahigh in-plane TC of 82.2 W (m K)-1 and a through-plane TC of 20.6 W (m K)-1, which were among the highest values ever reported for TCMs. Furthermore, the LM@BN bulks exhibited superior compressive and leakage-free performances, with a high compressive strength (5.2 MPa) and without any LM leakage even after being crushed. It was also demonstrated that the excellent TCs of the LM@BN bulks made them effectively cool high-power light emitting diode modules. This work opens up one promising pathway for the development of high-performance TCMs for thermal management in the electronics industry.

Permanent Shape Reconfiguration and Locally Reversible Actuation of a Carbon Nanotube/Ethylene Vinyl Acetate Copolymer Composite by Constructing a Dynamic Cross-Linked Network.

Given the rapid developments in modern devices, there is an urgent need for shape-memory polymer composites (SMPCs) in soft robots and other fields. However, it remains a challenge to endow SMPCs with both a reconfigurable permanent shape and a locally reversible shape transformation. Herein, a dynamic cross-linked network was facilely constructed in carbon nanotube/ethylene vinyl acetate copolymer (CNT/EVA) composites by designing the molecular structure of EVA. The CNT/EVA composite with 0.05 wt % CNT realized a steady-state temperature of ∼75 °C under 0.11 W/cm2 light intensity, which gave rise to remote actuation behavior. The dynamic cross-linked network along with a wide melting temperature offered opportunities for chemical and physical programming, thus realizing the achievement of the programmable three-dimensional (3D) structure and locally reversible actuation. Specifically, the CNT/EVA composite exhibited a superior permanent shape reconfiguration by activating the dynamic cross-linked network at 140 °C. The composite also showed a high reversible deformation rate of 11.1%. These features endowed the composites with the capability of transformation to 3D structure as well as locally reversible actuation performance. This work provides an attractive guideline for the future design of SMPCs with sophisticated structures and actuation capability.

Low-Voltage Actuator with Bilayer Structure for Various Biomimetic Locomotions.

Composites based on a shape-memory polymer doped with conductive particles are considered as soft actuators for artificial muscles and robots. Low-voltage actuating is expected to reduce equipment requirement and safety hazards, which requires a highly conductive particle content but weakens the reversible deformation. The spatial distribution of the conductive particle is key to decreasing the actuating voltage and maintaining the reversible deformation. Herein, an approach of fabricating a low-voltage actuator that can perform various biomimetic locomotions by spraying and hot pressing is reported. Carbon nanotubes (CNTs) are enriched inside the surface layer of poly(ethylene-co-vinyl acetate) (EVA) to form a high-density conductive network without degradation of the reversible deformation. The bilayer CNT/EVA actuator exhibits a reversible transformation of more than 10% even with 100 cycles, which requires an applied voltage of just 15 V. Taking advantage of the reprogrammability of the CNT/EVA actuator and reversible shift between the different shapes, different biomimetic locomotions (sample actuator, gripper, and walking robot) are demonstrated without any additional mechanical components. A scheme combining the electrical properties and the shape-memory effect provides a versatile strategy to fabricate low-voltage-actuated polymeric actuators, providing inspiration in the development of electrical soft actuators and biomimetic devices.

Ultra-Robust Thermoconductive Films Made from Aramid Nanofiber and Boron Nitride Nanosheet for Thermal Management Application.

The development of highly thermally conductive composites with excellent electrical insulation has attracted extensive attention, which is of great significance to solve the increasingly severe heat concentration issue of electronic equipment. Herein, we report a new strategy to prepare boron nitride nanosheets (BNNSs) via an ion-assisted liquid-phase exfoliation method. Then, silver nanoparticle (AgNP) modified BNNS (BNNS@Ag) was obtained by in situ reduction properties. The exfoliation yield of BNNS was approximately 50% via the ion-assisted liquid-phase exfoliation method. Subsequently, aramid nanofiber (ANF)/BNNS@Ag composites were prepared by vacuum filtration. Owing to the "brick-and-mortar" structure formed inside the composite and the adhesion of AgNP, the interfacial thermal resistance was effectively reduced. Therefore, the in-plane thermal conductivity of ANF/BNNS@Ag composites was as high as 11.51 W m-1 K-1, which was 233.27% higher than that of pure ANF (3.45 W m-1 K-1). The addition of BNNS@Ag maintained tensile properties (tensile strength of 129.14 MPa). Moreover, the ANF/BNNS@Ag films also had good dielectric properties and the dielectric constant was below 2.5 (103 Hz). Hence, the ANF/BNNS@Ag composite shows excellent thermal management performance, and the electrical insulation and mechanical properties of the matrix are retained, indicating its potential application prospects in high pressure and high temperature application environments.

Stretchable Liquid Metal-Based Conductive Textile for Electromagnetic Interference Shielding.

Conductive textiles (CTs) are promising electromagnetic interference (EMI) shielding materials. Nevertheless, limited stretchability and poor reliability restrict their potential applications in stretchable electronic devices because of the rigid conductive networks. Herein, a highly stretchable and reliable CT is developed for effective EMI shielding by designing a deformable liquid-metal (LM) coating and polydimethylsiloxane (PDMS) protective layer. The resultant PDMS-LM/Textile exhibits an outstanding EMI shielding efficiency (EMI SE) of 72.6 dB at a thickness of only 0.35 mm while maintaining EMI SEs of 66.0 and 52.4 dB under strains of 30 and 50%, respectively. The corresponding EMI SEs hold 91.7 and 80.3% retention after 5000 stretching-releasing cycles, respectively. The superior and durable EMI SE should be ascribed to the perfect connectivity and good deformability of conductive LM networks. Moreover, the LM coating has a robust fastness to the textile substrate, without any obvious decrease in EMI SE after 10 min of ultrasonic treatment and 100 peeling cycles because of the protective effect of the PDMS layer. This work provides a novel route to developing highly stretchable CTs for advanced EMI shielding applications, especially in the field of highly stretchable electronic devices.

Highly Stretchable and Sensitive Strain Sensor with Porous Segregated Conductive Network.

Flexible strain sensors based on elastomeric conductive polymer composites (ECPCs) play an important role in wearable sensing electronics. However, the achievement of good conjunction between broad detection range and high sensitivity is still challenging. Herein, a highly stretchable and sensitive strain sensor was developed with the formation of porous segregated conductive network in the carbon nanotube/thermoplastic polyurethane composite via a facile and nontoxic compression-molding plus salt-leaching method. The strain sensor with porous segregated conductive network exhibited perfect combination of ultrawide sensing range (800% strain), large sensitivity (gauge factor of 356.4), short response time (180 ms) and recovery time (180 ms), as well as superior stability and durability. The integrated porous structure intensifies the deformation of segregated conductive network when tension strain is applied, which benefits enhancement of the sensitivity. Our sensor could monitor not only subtle oscillation and physiological signals but also energetic human motions efficiently, revealing promising potential applications in wearable motion monitoring systems. This work provides a unique and effective strategy for realizing ECPCs based strain sensors with excellent comprehensive sensing performances.

Robustly Superhydrophobic Conductive Textile for Efficient Electromagnetic Interference Shielding.

Superhydrophobic electromagnetic interference (EMI) shielding textile (EMIST) is of great significance to the safety and long-term service of all-weather outdoor equipment. However, it is still challenging to achieve long-term durability and stability under external mechanical deformations or other harsh service conditions. Herein, by designing and implementing silver nanowire (AgNW) networks and a superhydrophobic coating onto a commercial textile, we demonstrate a highly robust superhydrophobic EMIST. The resultant EMIST shows a synergy of high water contact angle (160.8°), low sliding angle (2.9°), and superior EMI shielding effectiveness (51.5 dB). Remarkably, the EMIST still maintains its superhydrophobic feature and high EMI shielding level (42.6 dB) even after 5000 stretching-releasing cycles. Moreover, the EMIST exhibits strong resistance to ultrasonic treatment up to 60 min, peeling test up to 100 cycles, strong acidic/alkaline solutions, and different organic solvents, indicating its outstanding mechanical robustness and chemical durability. These attractive features of the EMIST are mainly a result of the joint action of AgNWs, carbon nanotubes, polytetrafluoroethylene nanoparticles, and fluoroacrylic polymer. This work offers a promising approach for the design of future durable, superhydrophobic EMISTs, which are capable of remaining fully functional against long-time exposure to extreme conditions, for example, wet and corrosive environments.

Robust carbon nanotube foam for efficient electromagnetic interference shielding and microwave absorption.

Lightweight and robust carbon nanotube (CNT)/chitosan (CS) foams were assembled by a facile unidirectional freeze-drying method in this work. The CNT/CS foam exhibited an excellent electromagnetic interference (EMI) shielding effectiveness (SE) of 37.6 dB while the density was only 17.6 mg·cm-3, and thus the corresponding specific SE was up to 8556 dB·cm2·g-1. The superior EMI shielding performance was mainly attributed to the perfect conductive networks. Additionally, the absorption coefficient of CNT/CS foam was up to 81.73% under high EMI SE of 37.6 dB, which was remarkable among the reported EMI shielding materials with comparable EMI shielding level. More importantly, the addition of CS significantly increased the compressive strength and modulus of CNT/CS foam to 34.1 KPa and 177.1 KPa, which were 84% and 149% higher than those for the pure CNT foam, respectively. These results indicate that the CNT/CS foam is an ideal high-efficient EMI shielding material, which has high potential applications in the fields of aerospace, automotive, and electronic devices.

Highly Efficient and Reliable Transparent Electromagnetic Interference Shielding Film.

Electromagnetic protection in optoelectronic instruments such as optical windows and electronic displays is challenging because of the essential requirements of a high optical transmittance and an electromagnetic interference (EMI) shielding effectiveness (SE). Herein, we demonstrate the creation of an efficient transparent EMI shielding film that is composed of calcium alginate (CA), silver nanowires (AgNWs), and polyurethane (PU), via a facile and low-cost Mayer-rod coating method. The CA/AgNW/PU film with a high optical transmittance of 92% achieves an EMI SE of 20.7 dB, which meets the requirements for commercial shielding applications. A superior EMI SE of 31.3 dB could be achieved, whereas the transparent film still maintains a transmittance of 81%. The integrated efficient EMI SE and high transmittance are superior to those of most previously reported transparent EMI shielding materials. Moreover, our transparent films exhibit a highly reliable shielding ability in a complex service environment, with 98 and 96% EMI SE retentions even after 30 min of ultrasound treatment and 5000 bending cycles (1.5 mm radius), respectively. The comprehensive performance that is associated with the facile fabrication strategy imparts the CA/AgNW/PU film with great potential as an optimized EMI shielding material in emerging optoelectronic devices, such as flexible solar cells, displays, and touch panels.

Efficient electromagnetic interference shielding of lightweight carbon nanotube/polyethylene composites via compression molding plus salt-leaching.

Carbon nanotube/high density polyethylene (CNT/HDPE) foam composites with high electrical conductivity and electromagnetic interference (EMI) shielding performance were developed by means of compression molding plus salt-leaching. The uniform porous structure and interconnected CNT networks throughout the cell backbones endowed the as-prepared foam composites with a significantly lower electrical percolation threshold (0.22 vol%) than that of the solid composites (0.84 vol%). Owing to the multiple reflections and scattering between the cell-matrix interfaces, the foam composites presented a superior specific EMI shielding effectiveness (EMI SE) of 104.3 dB cm3 g-1, 2.2 times higher than that of their solid counterpart. Besides this, the pore sizes of the CNT/HDPE foam composites could be easily tuned by controlling the particle size of the porogen. Also, the electrical conductivity and specific EMI SE increased with an increase in the cell diameter, which was attributed to the formation of a more perfect conductive network in the cell backbones. Our approach provides a novel idea for fabricating new lightweight EMI shielding materials, especially for aircraft and spacecraft applications.

Layer-Structured Design and Fabrication of Cyanate Ester Nanocomposites for Excellent Electromagnetic Shielding with Absorption-Dominated Characteristic.

In this work, we propose novel layer-structured polymer composites (PCs) for manipulating the electromagnetic (EM) wave transport, which holds unique electromagnetic interference (EMI) shielding features. The as-prepared PCs with a multilayered structure exhibits significant improvement in overall EMI shielding effectiveness (EMI SE) by adjusting the contents and distribution of electrical and magnetic loss fillers. The layer-structured PCs with low nanofiller content (5 wt % graphene nanosheets (GNSs) and 15 wt % Fe3O4) and a thickness of only 2 mm exhibited ultrahigh electrical conductivity and excellent EMI SE, reaching up to 2000 S/m and 45.7 dB in the X-band, respectively. The increased EMI SE of the layer-structured PCs was mainly based on the improved absorption rather than the reflection of electromagnetic waves, which was attributed to the "absorb-reflect-reabsorb" process for the incident electromagnetic waves. This work may provide a simple and effective approach to achieve new EMI shielding materials, especially for absorption-dominated EMI shielding.

Octadecylamine-Grafted Graphene Oxide Helps the Dispersion of Carbon Nanotubes in Ethylene Vinyl Acetate.

In this paper, the dispersion of carbon nanotube (CNT) in ethylene vinyl acetate (EVA) is demonstrated to be significantly improved by the addition of octadecylamine (ODA)-grafted graphene oxide (GO) (GO⁻ODA). Compared to the CNT/EVA composite, the resultant GO⁻ODA/CNT/EVA (G⁻CNT/EVA) composite shows simultaneous increases in tensile strength, Young's modulus and elongation at break. Notably, the elongation at break of the G⁻CNT/EVA composite still maintains a relatively high value of 1268% at 2.0 wt % CNT content, which is more than 1.6 times higher than that of CNT/EVA composite (783%). This should be attributed to the homogeneous dispersion of CNT as well as the strong interfacial interaction between CNT and EVA originating from the solubilization effect of GO⁻ODA. Additionally, the G⁻CNT/EVA composites exhibit superior electrical conductivity at low CNT contents but inferior value at high CNT contents, compared to that for the CNT/EVA composite, which depends on the balance of CNT dispersion and the preservation of insulating GO⁻ODA. Our strategy provides a new pathway to prepare high performance polymer composites with well-dispersed CNT.